Generally, as a display substrate for LED display devices, organic EL devices, a color filter substrate, a photovoltaic cell substrate, a glass plate is widely employed. However, the glass plate has such disadvantages as being easily broken, being non-bendable, being unsuitable for weight reduction due to its large specific weight. Therefore, plastic materials have been considered, as substitutes therefor.
As resin compositions for use in display device plastic substrates, there are known a resin composition comprising alicyclic epoxy resin, alcohol, and a curing catalyst (see e.g. Patent Document 1), a resin composition comprising alicyclic epoxy resin, a curing agent based on acid anhydride, partially esterified with alcohol, and a curing catalyst (see e.g. Patent Document 2), a resin composition comprising alicyclic epoxy resin, a curing agent based on acid anhydrite containing carboxylic acid (see e.g. Patent Document 3), etc. However, the plastic substrates formed of such resin compositions have significantly greater linear expansion coefficients than a thin film of Si or the like to be laminated thereon. For this reason, such mismatch of linear expansion coefficient causes thermal stress, strain, cracking and/or interfacial delamination of the formed layer, which cause, in turn, warp in the plastic substrates (see e.g. Non-Patent Document 1).
In view of the above, in recent years, it has been proposed to employ a transparent hybrid sheet consisting of a resin composition that contains alicyclic epoxy resin having an ester group, bisphenol A type epoxy resin, an acid anhydrate based curing agent, and a catalyst, and a glass cloth (see e.g. Patent Document 4), a transparent hybrid sheet consisting of a resin composition that contains alicyclic epoxy resin having an ester group, epoxy resin having a dicyclopentadiene skeleton and acid anhydride based curing agent and a glass cloth (see. e.g. Patent Document 5) or a transparent hybrid sheet consisting of bisphenol A type epoxy rein, bisphenol A novolac type epoxy resin and acid anhydride based curing agent and a glass cloth (see e.g. Patent Document 6).
With these transparent hybrid sheets, it is possible to reduce significantly the linear expansion coefficient, as compared with the plastic substrates formed of the resin compositions described in Patent Documents 1-3 described above. Yet, when these transparent hybrid sheets are put into use as display device plastic substrates, there occurs reduction in the display performance, due to the insufficient thermal resistance and significant optical anisotropy of the resins and due to the low flatness thereof, there also occur such problems as deterioration in the display quality.
To cope with these problems, the art has been studying the possibility of using 3,4,3′,4′-diepoxybicyclohexyl compound in the resin composition for use in the transparent hybrid sheet, in order to improve its properties as a display device plastic substrate (see e.g. Patent Document 7). Such transparent hybrid sheet as this is superior to the above-described transparent hybrid sheets disclosed in Patent Documents 4-6, in each and every respect of the thermal resistance, optical anisotropy and flatness.    Patent Document 1: Japanese Patent Application “Kokai” No. 6-337408    Patent Document 2: Japanese Patent Application “Kokai” No. 2001-59015    Patent Document 3: Japanese Patent Application “Kokai” No. 2001-59014    Patent Document 4: Japanese Patent Application “Kokai” No. 2004-51960    Patent Document 5: Japanese Patent Application “Kokai” No. 2005-146258    Patent Document 6: Japanese Patent Application “Kokai” No. 2004-233851    Patent Document 7: Japanese Patent Application “Kokai” No. 2005-206787    Non-Patent Document 1: “Monthly Display” January, 2000 issue, p. 35.